Study of phase sensitive X-ray imaging and its applications in materials science and medical imaging.

The conventional X-ray radiography relies on absorption for contrast formation in its image. This type of radiography is able to distinguish between hard (high Z) and soft (low Z) materials but it has severe limitations when it comes to imaging or distinguishing between of soft materials like polymers, carbon fiber composites and soft biological tissues due to low absorption for such materials. 
In recent years, a new imaging technique named Phase contrast imaging is being developed to remove the limitations of conventional X-ray imaging and it promises to revolutionize the way X-ray imaging particularly for soft material imaging has been conducted till now. Unlike absorption based X-ray radiography where absorption is dependent on imaginary part of refractive index, the contrast produced in X-ray phase contrast imaging depends on the real part of refractive index. Though this technique is under active investigation worldwide using large X-ray sources like synchrotrons, limited work has been done on exploiting this technique using a laboratory based X-ray source. The main requirement of phase contrast imaging is that source should be coherent. Ideally source should have both with spatial and temporal coherence but it has been shown that for many of the experiments phase contrast can be done with source having only partial coherence, which is only spatial coherence though with somewhat degraded image quality. This has led to the use to microfocus sources for such experiments.
The main motivation of this study has been to explore the use of laboratory based microfocus source for phase contrast imaging and apply it for the study of some new class of problem which has never before been tried. As a part of this study, a microfocus based X-ray phase contrast imaging setup has been developed at Purnima laboratory, BARC using dedicated detector setup first time within the country. The experimental work has been preceded by extensive theoretical simulations for finding optimal conditions for high quality phase contrast images. The dependence of the phase contrast on source size, detector resolution, source to sample distance and sample to detector distance on image quality has been studied in a quantitative manner. Based on these simulations an optimum condition for obtaining best phase contrast image has been established. This criterion has been applied in doing experiments on phase contrast imaging on a variety of samples.
I have done the experiments for several new materials such as pyrocarbon (PyC) & silicon carbide coated zirconia microspheres and PyC coated alumina microspheres using X-ray phase contrast imaging technique. These objects are coated with low Z material and have poor X-ray absorption and consequently these coatings are not visible in conventional absorption based imaging. A method has been established for quantitative analysis of these results and found out coating thickness of PyC coated samples from these images. The experimental results also describe phase contrast effects on carbon fiber, carbon composite structures and some biological materials such as honey bee, mosquito, cockroach and dry leaves. The experimental work also has been done on X-ray phase imaging by using synchrotron source at ELETTRA, Italy. This experiment has been done for the inter-comparison of phase contrast images of same samples using both microfocus (polychromatic X-ray) and synchrotron (monochromatic X-ray) sources.